1. Field of the Invention
The present invention relates to autopilot steering systems for marine vessels and more specifically to an autopilot that selects an optimum rudder activity position to minimize propulsion losses due to hull and rudder drag.
2. Description of the Prior Art
The operation efficiency of a marine vessel depends in large part on minimizing propulsion losses generated by resistance to forward motion of the vessel. The total vessel resistance of hull and rudder. Hull resistance is substantially a constant being function of hull design and loading. Therefore, in operation, only the rudder activity may be controlled to minimize overall resistance to forward motion.
For given operating conditions, resistance of a vessel to forward motion increases as yaw increases. Increasing the rudder activity in an effort to decrease yaw also increases resistance to forward motion. Therefore, optimum operating efficiency requires a balance between rudder activity and allowable yaw.
A prior autopilot seeking to accomplish the objective of balancing allowable yaw and rudder activity to yield a minimum resistance to forward motion is embodied in U.S. Pat. No. 4,074,648 issued Feb. 21, 1978 to Robert Reid et al and assigned to the assignor of the present invention. In Reid et al, the autopilot adjusts the sensitivity of the vessel's steering system to accommodate changes in speed, sea and wind conditions to provide a balance between yaw motion and rudder activity. However, in Reid et al, a detailed knowledge of the vessel's dynamic performance characteristics and extensive computer simulation is required to formulate the equations used to optimize the operating efficiency of any given vessel. Further, if the simulations do not match a vessel's actual performance, there are no corrections or calibration available to adjust the predicted performance to the actual performance so that operating efficiency of the vessel may be maximized.
In the present invention, a digital computer and its associated algorithm are adaptable to many types of vessels. No prior knowledge of a given vessel's characteristics are required and no computer simulation of a vessel's operating performance is required to practice the present invention.